1. Field of the Invention
The present invention relates to a noise-absorbing structure for a cable reel. A cable reel is used in steering equipment for automobiles or in similar equipment, and secures electrical connections between fixed elements and mobile elements through a flat cable. The flat cable is stored in a cable-storing enclosure in a spiraled condition. More particularly, the invention concerns an improvement in the assembly structures of a noise-absorbing material, with which a flat cable is put in contact via a spring force.
2. Description of Background Information
As shown in FIG. 1, this type of cable reel has a ring-shaped cable-reel enclosure 3, including a mobile element 1 which rotates with a steering wheel, and a fixed element 2 which is fixed around an axis linked to the car body. A flat cable 4 is contained in the cable-reel enclosure 3 in a spiraled condition. One end of the flat cable 4 is connected to a conductor element linked to the mobile element 1, while its other end is connected to a conductor element linked to the fixed element 2. In the above cable reel 4, when the steering wheel is rotated clockwise or counterclockwise, the flat cable is either wound or unwound. In this manner, equipment mounted on the steering wheel, e.g. an airbag, and electrical power sources on the side of the car body, are electrically connected.
In the above cable reel, when the flat cable 4 is wound or unwound, the side rims of the helical flat cable rub against the surfaces of cable reel enclosure 3 which are in contact with the corresponding side rim. This rubbing emits unpleasant noises. Further, the vibrations caused by idling or driving a car will make the flat cable 4 move to-and-fro along the axis of steering wheel. The flat cable will then bump against the rubbing surfaces, thereby further creating unpleasant noises.
In order to reduce unpleasant rubbing noises, Japanese Utility Model HEI 6-36040 disclosed a mechanism shown in FIGS. 2A and 2B, in which a noise-absorbing smooth sheet 5, e.g. a tetrafluoroethylene resin sheet, is adhered to a top rubbing surface and a bottom rubbing surface, respectively, or only to the bottom rubbing surface 2a, with an adhesive material 6. As an alternative to direct adhesive adhesion as described above, the noise-absorbing smooth sheet and the rubbing surfaces can be fixed mechanically, as shown in FIG. 3: the internal face of outer circular wall 2b of the fixed element 2 is provided with a protrusion 2c; the noise-absorbing smooth sheet 5 is then superposed on a supporting plate 7; and the entire structure is inserted between the bottom rubbing surface 2aand the protrusion 2c. Alternatively, as shown in FIG. 4 for a variant, a supporting plate 7xe2x80x2 is provided with a hook portion 7axe2x80x2, whereas the bottom rubbing surface 2a is provided with a stopper hole 2d. The noise absorbing smooth sheet 5 is then superposed on, and adhered to, the variant supporting plate 7xe2x80x2, and the entire structure is fixed to the bottom rubbing surface 2a by inserting the hook portion 7axe2x80x2 into the stopper hole 2d. 
In the structures shown in FIGS. 3 and 4, a clearance C is formed between the noise-absorbing smooth sheet 5 and the supporting plate 7, and also between the internal face of outer circular wall 2b of the fixed element 2 and an inner circular wall (not shown in the Figures), respectively. Accordingly, vibrations caused by driving the car bias the noise-absorbing smooth sheet 5 and the supporting plate 7 diametrically, so that the supporting plate 7 comes into contact with the outer circular wall 2b and the inner circular wall, and generates unpleasant vibration noises. In particular, when the motor is idled, the unpleasant noises caused by vibration sound fairly loud. Besides, when there are clearances C on the external and internal circular rims of both the noise-absorbing smooth sheet 5 and supporting plate 7, the noiseabsorbing smooth sheet 5 rotates together with the flat cable which is in contact therewith. The noise-absorbing smooth sheet 5 then tends to jolt also in the circumferential direction of the rotation. Rubbing noises may thus be created.
If the supporting plate 7 is downsized with regard to the noise-absorbing smooth sheet 5, the latter will come into contact with the circular walls, before the support plate 7 will. The vibration noises caused by the support plate 7 may thus be reduced. However, when manufacturing the ring-shaped sheet, the noise-absorbing smooth sheet 5 and the supporting sheet 7 are integrally formed by stamping. Accordingly, it is difficult to downsize only the supporting plate 7 when manufacturing. If they are made separately and secured together, production will become costlier.
When the noise-absorbing smooth sheet 5 shown in FIG. 2B is directly adhered to the rubbing face with an adhesive material 6, the former does not move, thereby generating no vibration noise. However, the noise-absorbing smooth sheet 5 and the adhesive material 6 must then be preliminarily adhered and layered. Moreover, a process step of adhering the adhesive material 6 to the rubbing face must be added in the operation.
An object of the present invention is therefore to provide a cable reel in which the noise-absorbing smooth sheet is fixed to the rubbing face of the cable reel, without being adhered thereto directly. Further, the noise-absorbing smooth sheet and the supporting plate are formed integrally so that the process steps are reduced. This structure prevents the generation of contact noises, which would otherwise be created when the smooth sheet and the supporting plate abut against the circular walls and base wall.
To solve the above problem, there is provided a noise-absorbing structure for a cable reel, the cable reel including a cable enclosure having a ring shape with a diametrically larger inner circular face and a diametrically smaller inner circular face. The cable enclosure includes a noise-absorbing material formed of a noise-absorbing smooth sheet and a supporting plate, and the diametrically larger inner circular face is unitarily provided with at least two holding tabs arranged substantially at equal intervals in the circumferential direction, such that the holding tabs immobilize the noise-absorbing material by holding the noise-absorbing smooth sheet.
Suitably, the at least two holding tabs include three or four holding tabs. The diametrically smaller inner circular face may also be provided unitarily with at least two, suitably three or four, holding tabs arranged in the circumferential direction and spaced apart with substantially the same distance therebetween.
In the above structure, the cable enclosure may further include a fixed element, and a mobile element mounted thereon in a freely rotatable way, so as to form a ring-shaped enclosure at least including an outer circular wall, an inner circular wall and a base wall.
In a preferred embodiment, the ring-shaped enclosure with the base wall is provided with a notch having two opposing side faces which extend inwardly from the outer circular wall. The noise-absorbing material is then sized to the same shape as the base wall and is superposed thereon, and the two opposing side faces include holding tabs which immobilize the noise-absorbing material by holding the noise-absorbing smooth sheet.
Preferably still, the base wall of the fixed element is provided with rapping holes corresponding to the holding tabs, and the rapping holes serve as checking holes to check whether or not the noise-absorbing material is mounted in the cable enclosure.
There is also provided a cable reel including a noise-absorbing structure, the cable reel including a cable enclosure having a ring shape with a diametrically larger inner circular face and a diametrically smaller inner circular face, wherein the cable enclosure includes a noise-absorbing material formed of a noise-absorbing smooth sheet and a supporting plate, and the diametrically larger inner circular face is unitarily provided with at least two holding tabs arranged in the circumferential direction with substantially the same distance apart therebetween, such that the holding tabs immobilize the noise-absorbing material by holding the noise-absorbing smooth sheet. The cable enclosure further includes a flat cable disposed on the noise-absorbing material in a wound state. The flat cable has two ends in the length direction, one end thereof being fixed to a rotatable mobile element and the other end thereof being fixed to a fixed element, so that the flat cable is wound or unwound depending on the rotation of the mobile element.
There is further provided a steering wheel incorporating a noise-absorbing structure for cable reel, the cable reel including a cable enclosure having a ring shape with a diametrically larger inner circular face and a diametrically smaller inner circular face. The cable enclosure includes a noise-absorbing material formed of a noise-absorbing smooth sheet and a supporting plate, and the diametrically larger inner circular face is unitarily provided with at least two holding tabs arranged in the circumferential direction with substantially the same distance apart therebetween, such that the holding tabs immobilize the noise-absorbing material by holding the noise-absorbing smooth sheet.
In the above noise-absorbing structure, if only the bottom side rim of the flat cable is in contact with the rubbing bottom face, the holding tabs are formed on the outer circular wall and/or inner circular wall near the rubbing base wall. When, in addition, the upper side rim of the flat cable is in contact with the upper rubbing face, the holding tabs may be provided on the circular walls adjacent to the upper rubbing face.
For example, holding tabs may be provided on the outer circular wall of the fixed element. These holding tabs put into contact the internal circular rim of noise-absorbing smooth sheet with the inner circular wall, so that the sheet is immobilized. Alternatively, the holding tabs may be provided on the outer circular wall and the inner circular wall. The holding tabs then hold both the external circular rim of the noise-absorbing smooth element and the internal circular rim thereof.
The holding tabs are preferably in the form of a hemisphere. The contact surface between the holding tabs and the noise-absorbing smooth sheet is thus small, and the rubbing surface is also rendered small. Accordingly, wear on the noise-absorbing smooth sheet is reduced, and the durability thereof is enhanced.
Preferably, the noise-absorbing smooth sheet is made by coating highly smooth tetrafluoroethylene resin on an elastic and flexible sheet such as a rubber or resin sheet. Suitably, the noise-absorbing smooth sheet is incorporated with a support plate made of polyethyleneterephthalate or polyethylene in a mold, to form a torus- or ring-shaped product. The tip portion of the holding tabs is in contact with the outer circular rim and/or inner circular rim of the elastic and flexible noise-absorbing sheet, so that the holding tabs are firmly fitted.
Advantageously, the inventive noise-absorbing material can be fitted with the holding tabs while it is in contact therewith, without causing any creaking.
When the holding tabs are formed on the outer and/or inner circular walls substantially with a same pitch therebetween, not only the noise-absorbing smooth sheet, but also the support plate is immobilized in the diametrical direction by the holding tabs. When the automobile engine is run or idled, it causes vibrations, and creates noises when the support plate clatters against the circular walls. However, the inventive structure can prevent or reduce such vibration noises.
Moreover, the noise-absorbing material is also immobilized in the circumferential direction by the holding tabs. Usually, when the noise-absorbing material is moved in the circumferential direction, creaking is created by the rubbing face. However, this creaking is also prevented by virtue of the holding tabs of the invention.
Further yet, as no adhesive is used for fixing, the process of installing the noise-absorbing material is rendered easier, and productivity is enhanced.
The fixed element has a base wall and is provided with a notch extending inwardly from the outer circular rim so as to form a U-shape having two opposing side faces on the bottom face. Part of the outer circular portion of noise-absorbing material is then sized up in the same shape as the bottom face and superposed thereon. In this case, the two opposing side faces may include holding tabs. The holding tabs then hold the rim faces of the noise-absorbing smooth sheet forming the noise-absorbing material.
The holding tabs are provided on the outer and/or inner circular walls. Correspondingly, rapping holes for the holding tabs are formed in the base wall of the fixed element. These holes are then used for checking whether or not the noise-absorbing material is mounted in the cable reel. In other words, as the outer circular wall and the inner circular wall are integrally provided with the base wall, the rapping holes are perforated in the base wall, in order to form the holding tabs. By virtue of this configuration, the noise-absorbing material can be seen from outside, also through these rapping holes. In this manner, the presence of noise-absorbing smooth sheet can be checked after the cable reel has been mounted.